Autoloading firearms in which the bolt is held only by spring pressure and the inertia of the mass of the bolt against the barrel to prevent premature opening when firing (principally known as "blow back" firearms) are known. External forces applied to such firearms, particularly upon the butt plate when the muzzle is elevated, can cause the bolt to move rearward prior to firing to unintentionally unload the firearm. This is particularly detrimental in the case of police-type service firearms.
It is also desirable to lock the firing pin against movement toward a cartridge in the firing chamber of the firearm unless the trigger is pulled.